Perspective: Molten core optical fiber fabrication—A route to new materials and applications

The molten core method, whereby a precursor core phase melts at the draw temperature of the cladding glass that encapsulates it, has proven to be a remarkably versatile approach to realize novel optical fibers. Employed globally for both scientific inquiry and practical applications, it is arguably the only approach that leads to long lengths of novel material fiber with both crystalline and glassy cores. This article reviews the history of the process, the ever-broadening range of compositions, the unique applications that have been enabled, and provides a perspective on current challenges and future opportunities.